Currently, nonaqueous electrolyte secondary batteries typified by lithium ion secondary batteries, particularly lithium secondary batteries, are widely mounted on portable terminals, and the like. For these nonaqueous electrolyte secondary batteries, mainly LiCoO2 is used as a positive active material. However, the discharge capacity of LiCoO2 is about 120 to 130 mAh/g.
As a material of a positive active material for a lithium secondary battery, a solid solution of LiCoO2 and other compounds is known. Li[Co1−2xNixMnx]O2 (0<x≤1/2), a solid solution having an α-NaFeO2 type crystal structure and formed of three components: LiCoO2, LiNiO2 and LiMnO2, has been published in 2001. LiNi1/2Mn1/2O2 or LiCo1/3Ni1/3Mn1/3O2 that is one example of the aforementioned solid solution has a discharge capacity of 150 to 180 mAh/g, and is also excellent in terms of charge-discharge cycle performance.
In contrast with so called a “LiMeO2-type” active material as described above, so called a “lithium-excess-type” active material is known in which the composition ratio Li/Me of lithium (Li) to the ratio of a transition metal (Me) is larger than 1, with Li/Me being, for example, 1.25 to 1.6 (see, for example, Patent Document 1 and Patent Document 2). This material can be represented by Li1+αMe1−αO2 (α>0). Here, β=(1+α)/(1−α) when the composition ratio Li/Me of lithium (Li) to the ratio of a transition metal (Me) is β, and therefore, for example, α=0.2 when Li/Me is 1.5.
Patent Document 1 describes on the active material “the intensity ratio of the diffraction peak of the (003) plane to the diffraction peak of the (104) plane in X-ray diffraction measurement is I(003)/I(104)≥1.56 before charge-discharge, and I(003)/I(104)>1 at the end of discharge”.
Further, the positive active material for a lithium secondary battery containing a lithium transition metal composite oxide in which the half widths of the diffraction peak of the (003) plane and the (104) plane in X-ray diffraction measurement are specified (see Patent Documents 3 to 5) are known.
Patent Document 3 describes “In a nonaqueous electrolyte secondary battery including a positive electrode containing a lithium-transition metal composite oxide as a positive electrode material, a negative electrode and nonaqueous electrolyte, wherein a compound which is a lithium-transition metal composite oxide including at least Ni, Co and Mn and in which a half width of the peak present in a range of 2θ=18.71±0.25°, measured by a powder X-ray diffraction measurement using CuKα as a radiation source is 0.22° or less, is used as the positive electrode material”. As an object of the invention, “To provide a nonaqueous electrolyte secondary battery which has an initial discharge capacity improved by improving a positive electrode material and has excellent cycle performance by suppressing a reduction of discharge capacity in repeating charge-discharge” is described.
Patent Document 4 describes “A lithium-nickel-manganese-cobalt composite oxide of a layer structure having chemical composition of LiaNixMnyCozO2+b (x+y+z=1, 1.00<a<1.3, 0≤b<0.3) in which diffraction peak angles 2θ of a (003) plane and a (104) plane in the Miller index hkl of a powder X-ray diffraction using a CuKα radiation source are 18.65° or more and 44.50° or more, respectively and both of half widths of the diffraction peaks of these planes are 0.18° or less, and further diffraction peak angles 2θ of a (108) plane and a (110) plane are 64.40° and 65.15° or more, respectively and both of half widths of the diffraction peaks of these planes are 0.18° or less”. As an object of the invention, “To provide a material for a positive active material which can impart a high discharge capacity, a high current load performance and high reliability (enhanced life) to the lithium ion secondary battery” is described.
Patent Document 5 describes “A lithium secondary battery including a current collector, and an active material layer containing an active material particle and held in the current collector, wherein the active material particle is a secondary particle formed by aggregating a plurality of primary particles of a lithium transition metal oxide, and constitutes a hollow structure having a hollow portion formed on the inner side of the secondary particle and a shell portion surrounding the hollow portion, and a through-hole penetrated from the outside to the hollow portion is formed in the secondary particle, and in a powder X-ray diffraction pattern of the active material particle, a ratio (A/B) of a half width A of a diffraction peak obtained by a (003) plane to a half width B of a diffraction peak obtained by a (104) plane satisfies the following formula: (A/B)≤0.7.”. As an object of the invention, to provide a lithium secondary battery which can exert a required power even in a low SOC region, improve travelling performance of hybrid automobile and electric automobiles, and reduce the number of batteries for securing a required amount of energy” is described.